RESULTS: Saccular dural diverticula (type I, n = 28) caused by defects of both dural layers, dissections between dural layers (type II, n = 29) due to defects of the inner layer, and dural ectasias (type III, n = 9) related to structural changes of the dura were distinguished. For all types, symptoms consisted of local pain followed by signs of radiculopathy or myelopathy, while one patient with dural ectasia presented a low-pressure syndrome and 10 patients with dural dissections additional spinal cord herniation. Type I and type II pathologies required occlusion of their dural defects via extradural (type I) or intradural (type II) approaches. For type III pathologies of the dural sac no surgerywas recommended. Favorable results were obtained in all 14 patients with type I and 13 of 15 patients with type II pathologies undergoing surgery.

CONCLUSION: The majority of dural pathologies involving root sleeves remain asymptomatic, while those of the dural sac commonly lead to pain and neurological symptoms. Type I and type II pathologies were treated with good long-term results occluding their dural defects, while ectasias of the dural sac (type III) were managed conservatively.

A subset of patients with Chiari I malformation demonstrate patent subarachnoid spaces around the cerebellum, indicating that reduced posterior fossa volume alone does not account for tonsillar descent. The authors distinguish two subsets of Chiari I malformation patients based on the degree of “posterior fossa crowdedness” on MRI.

METHODS Two of the coauthors independently reviewed the preoperative MR images of 49 patients with Chiari I malformation and categorized the posterior fossa as “spacious” or “crowded.” Volumetric analysis of posterior fossa structures was then performed using open-source DICOM software. The preoperative clinical and imaging features of the two groups were compared.

RESULTS The posterior fossae of 25 patients were classified as spacious and 20 as crowded by both readers; 4 were incongruent. The volumes of the posterior fossa compartment, posterior fossa tissue, and hindbrain (posterior fossa tissue including herniated tonsils) were statistically similar between the patients with spacious and crowed subtypes (p = 0.33, p = 0.17, p = 0.20, respectively). However, patients in the spacious and crowded subtypes demonstrated significant differences in the ratios of posterior fossa tissue to compartment volumes as well as hindbrain to compartment volumes (p = 0.001 and p = 0.0004, respectively). The average age at surgery was 29.2 ± 19.3 years (mean ± SD) and 21.9 ± 14.9 years for spacious and crowded subtypes, respectively (p = 0.08). Syringomyelia was more prevalent in the crowded subtype (50% vs 28%, p = 0.11).

CONCLUSIONS The authors’ study identifies two subtypes of Chiari I malformation, crowded and spacious, that can be distinguished by MRI appearance without volumetric analysis. Earlier age at surgery and presence of syringomyelia are more common in the crowded subtype. The presence of the spacious subtype suggests that crowdedness alone cannot explain the pathogenesis of Chiari I malformation in many patients, supporting the need for further investigation.

Previous studies have indicated an association of Chiari malformation Type I (CM-I) and a small posterior fossa. Most of these studies have been limited by 2D quantitative methods, and more recent studies utilizing 3D methodologies are time-intensive with manual segmentation. The authors sought to develop a more automated tool to calculate the 3D posterior fossa volume, and correlate its changes after decompression with surgical outcomes.

METHODS A semiautomated segmentation program was developed, and used to compare the pre- and postoperative volumes of the posterior cranial fossa (PCF) and the CSF spaces (cisterna magna, prepontine cistern, and fourth ventricle) in a cohort of pediatric patients with CM-I. Volume changes were correlated with postoperative symptomatic improvements in headache, syrinx, tonsillar descent, cervicomedullary kinking, and overall surgical success.

CONCLUSIONS A greater increase in the postoperative PCF volume, and specifically an increase in the cisterna magna volume, was associated with a greater likelihood of clinical improvements in headache and tonsillar descent in patients with CM-I. Larger increases in the caudal portion of the posterior fossa volume were also associated with a greater likelihood of improvement in syrinx and cervicomedullary kinking.

We have previously proposed that pineal cysts (PCs) may result in crowding of the pineal recess, causing symptoms due to compression of the internal cerebral veins and central venous hypertension. In the present study, we compared clinical outcome of different treatment modalities in symptomatic individuals with non-hydrocephalic PCs.

Methods The study included all patients managed surgically for non-hydrocephalic PCs in our Department of Neurosurgery over a 10-year period. We applied a questionnaire to determine occurrence of symptoms before and after surgery, which allowed the use of a grading scale for symptom severity. Magnetic resonance imaging (MRI) biomarkers indicative of central venous hypertension were assessed before and after surgery.

Results Relief of symptoms after surgery was most efficiently obtained by complete microsurgical cyst removal [n = 15; no (0/15), some (1/15) or marked (14/15) improvement], and to a lesser extent by microsurgical cyst fenestration [n = 6; no (2/6), some (4/6) or marked (0/6) improvement]. Shunt surgery was not successful [n = 6; no (5/6), some (1/6) or marked (0/6) improvement]. In all patients, the proposed MRI biomarkers gave evidence of central venous hypertension (PC grades 2–4).

This study identifies quantitative imaging-based measures in patients with Chiari malformation Type I (CM-I) that are associated with positive outcomes after suboccipital decompression with duraplasty.

Methods Fifteen patients in whom CM-I was newly diagnosed underwent MRI preoperatively and 3 months postoperatively. More than 20 previously described morphological and physiological parameters were derived to assess quantitatively the impact of surgery. Postsurgical clinical outcomes were assessed in 2 ways, based on resolution of the patient’s chief complaint and using a modified Chicago Chiari Outcome Scale (CCOS). Statistical analyses were performed to identify measures that were different between the unfavorable- and favorable-outcome cohorts. Multivariate analysis was used to identify the strongest predictors of outcome.

Results The strongest physiological parameter predictive of outcome was the preoperative maximal cord displacement in the upper cervical region during the cardiac cycle, which was significantly larger in the favorable-outcome subcohorts for both outcome types (p < 0.05). Several hydrodynamic measures revealed significantly larger preoperative-topostoperative changes in the favorable-outcome subcohort. Predictor sets for the chief-complaint classification included the cord displacement, percent venous drainage through the jugular veins, and normalized cerebral blood flow with 93.3% accuracy. Maximal cord displacement combined with intracranial volume change predicted outcome based on the modified CCOS classification with similar accuracy.

Conclusions Tested physiological measures were stronger predictors of outcome than the morphological measures in patients with CM-I. Maximal cord displacement and intracranial volume change during the cardiac cycle together with a measure that reflects the cerebral venous drainage pathway emerged as likely predictors of decompression outcome in patients with CM-I.

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Colloid cysts are rare, histologically benign lesions that may result in obstructive hydrocephalus and death. Understanding the natural history of colloid cysts has been challenging given their low incidence and the small number of cases in most reported series. This has complicated efforts to establish reliable prognostic factors and surgical indications, particularly for asymptomatic patients with incidental lesions. Risk factors for obstructive hydrocephalus in the setting of colloid cysts remain poorly defined, and there are no grading scales on which to develop standard management strategies.

Methods The authors performed a single-center retrospective review of all cases of colloid cysts of the third ventricle treated over nearly 2 decades at Washington University. Univariate analysis was used to identify clinical, imaging, and anatomical factors associated with 2 outcome variables: symptomatic clinical status and presentation with obstructive hydrocephalus. A risk-prediction model was defined using bootstrapped logistic regression. Predictive factors were then combined into a simple 5-point clinical scale referred to as the Colloid Cyst Risk Score (CCRS), and this was evaluated with receiver-operator characteristics.

Results The study included 163 colloid cysts, more than half of which were discovered incidentally. More than half of the incidental cysts (58%) were followed with surveillance neuroimaging (mean follow-up 5.1 years). Five patients with incidental cysts (8.8%) progressed and underwent resection. No patient with an incidental, asymptomatic colloid cyst experienced acute obstructive hydrocephalus or sudden neurological deterioration in the absence of antecedent trauma. Nearly half (46.2%) of symptomatic patients presented with hydrocephalus. Eight patients (12.3%) presented acutely, and there were 2 deaths due to obstructive hydrocephalus and herniation. The authors identified several factors that were strongly correlated with the 2 outcome variables and defined third ventricle risk zones where colloid cysts can cause obstructive hydrocephalus. No patient with a lesion outside these risk zones presented with obstructive hydrocephalus. The CCRS had significant predictive capacity for symptomatic clinical status (area under the curve [AUC] 0.917) and obstructive hydrocephalus (AUC 0.845). A CCRS ≥ 4 was significantly associated with obstructive hydrocephalus (p < 0.0001, RR 19.4).

Conclusions Patients with incidentally discovered colloid cysts can experience both lesion enlargement and symptom progression or less commonly, contraction and symptom regression. Incidental lesions rarely cause acute obstructive hydrocephalus or sudden neurological deterioration in the absence of antecedent trauma. Nearly one-half of patients with symptomatic colloid cysts present with obstructive hydrocephalus, which has an associated 3.1% risk of death. The CCRS is a simple 5-point clinical tool that can be used to identify symptomatic lesions and stratify the risk of obstructive hydrocephalus. External validation of the CCRS will be necessary before objective surgical indications can be established. Surgical intervention should be considered for all patients with CCRS ≥ 4, as they represent the high-risk subgroup.

Up to now, only little is known about hydrocephalus (HC) in vein of Galen malformation (VGM).We want to present the different etiologies and our long-term experience (1992–2015) in the management of HC.

Methods Out of 44 treated children with VGM, we retrospectively reviewed all cases with HC.We analyzed the etiologies, our treatment results and complications.

Results Twenty-one children (48 %) presented either with HC or developed it over time. In 21% of those cases, high venous pressure was presumably the sole cause. Until 2009, seven of them received ventriculoperitoneal (VP) shunting; six of those resulted in severe postoperative complications. The remaining children have been treated successfully by endovascular embolization. Five out of the 44 children (11 %) developed HC after intraventricular hemorrhage. In four cases, those children were treated with positive results by using transient external ventricular drainages. In one case a VP shunt with highest valve pressure was inserted. Another four children (9 %) presented with aqueductal stenosis-related HC caused by either dilated venous outflow or space-occupying coil masses after embolization. The latter case was successfully treated by ventriculocisternostomy, whereas endovascular treatment decreased the venous outflow in size and thus resolved the HC in the other cases. In the remaining cases (7 %), atrophy due to melting brain syndrome led to HC ex vacuo.

Conclusions HC in VGM is a common phenomenon with several etiologies requiring different treatments. In most cases, embolization of the VGM as sole treatment is completely sufficient in order to decrease high venous pressure. However, certain other causes of HC should be treated in an interdisciplinary setting by specialized neurosurgeons.

Whether a difference in morphology of the infratentorial space is associated with hemifacial spasm is not well understood. The aim of this study was to analyze the three-dimensional conformation of the infratentorial space and evaluate any possible contribution of morphological characteristics to the development of neurovascular compression leading to hemifacial spasm.

Methods We enrolled 25 patients with hemifacial spasm and matched them by age and sex to controls. The extent of the three-dimensional axes and the volume of the infratentorial space were measured using image analysis software for three-dimensional MRI.We evaluated the correlation between a morphological difference in the infratentorial space and changes in vascular configuration in the brain stem.

Results We found no statistical difference in volumetric analyses. The mean aspect ratio on the coronal plane (the ratio of the Z to X extent) of the infratentorial space in patients with hemifacial spasm was significantly lower (p < 0.01) than that in controls, as was the mean aspect ratio on the sagittal plane (the ratio of Z to Yextent, p <0.01). A smaller sagittal aspect ratio was correlated (p < 0.05) with greater lateral deviation of the basilar artery.

Conclusions Our results suggest that flatness of the superior-inferior dimension of the infratentorial space is an anatomical feature that characterizes patients with hemifacial spasm. We hypothesize that this unique structural variation may exaggerate the lateral deviation of the vertebrobasilar arteries due to arteriosclerosis and exacerbate the space competition among vessels and cranial nerves.

There is no previous prospective study on the outcome of surgical decompression of intracranial arachnoid cysts (AC).

OBJECTIVE: To investigate if surgical fenestration for AC leads to change in patients’ health-related quality of life.

METHODS: Prospective study including 76 adult patients operated for AC. Patients responded to Short Form-36 and Glasgow Benefit Inventory quality of life questionnaires, and to visual analogue scales, assessing headache and dizziness pre- and postoperatively. Patient scores were compared with those of a large sample of healthy individuals.

RESULTS: Preoperatively, 84.2% of the patients experienced headache and 70.1% dizziness. Mean pre- versus postoperative Visual Analogue Scale scores for headache and dizziness dropped from 45.6 to 25.7 and from 35.2 to 12.2, respectively. Preoperative Short Form-36 scores were significantly below age norms in all subscales, but improved after surgery into normal range in 7 out of 8 subscales for middle-aged and older patients. Younger patients’ scores remained lower than age norm in 6 out of 8 subscales. A significant postoperative improvement was seen in 3 out of 4 Glasgow Benefit Inventory subscales. Improvement in headache and/or dizziness, but not preoperative cyst size or reduction in cyst volume, correlated with improvement in 6 out of 8 Short Form-36 subscales and 3 out of 4 Glasgow Benefit Inventory subscales. Only 1 patient experienced a severe complication causing permanent invalidity.

CONCLUSION: Surgery for AC can be performed with a fairly low risk of complications and yields significant improvement in quality of life correlated to postoperative improvement in headache and dizziness. These findings may justify a more liberal approach to surgical treatment for AC.

The pathogenesis of syringomyelia associated with Chiari malformation type I (CM-I) is unclear. Theories of pathogenesis suggest the cerebellar tonsils may obstruct CSF flow or alter pressure gradients, or their motion might act as a piston to increase CSF pressure in the spinal subarachnoid space. This study was performed to measure cerebellar tonsillar and hindbrain motion in CM-I and assess the potential contributions to syrinx formation.

Methods Sixty-four CM-I patients and 25 controls were retrospectively selected from a clinical database, and all subjects had undergone cardiac-gated cine balanced fast-field echo MRI. There were a total of 36 preoperative CM-I scans, which consisted of 15 patients with and 21 patients without syringomyelia. Nineteen patients underwent paired pre- and postoperative imaging. Anteroposterior (AP) and superoinferior (SI) movements of the tip of the cerebellar tonsils, obex, fastigium of the fourth ventricle, pontomedullary junction, and cervicomedullary junction were measured. The distance between the fastigium and tip of the tonsils was used to calculate tonsillar tissue strain.

Conclusions Cerebellar tonsillar motion may be a potential marker of CM-I and may have use in tailoring surgical procedures. The lack of association with syringomyelia suggests that tonsillar motion alone is not the driver of syrinx formation. Tonsillar tissue strain may play a part in the pathophysiology of Valsalva headaches.

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Klippel-Feil syndrome (KFS) is characterized by congenital vertebral fusion of the cervical spine and a wide spectrum of associated anomalies. In patients with KFS with basilar invagination (BI), compression of the brainstem and upper cervical cord results in neurological deficits, and decompression and occipitocervical reconstruction are required. The highly varied anatomy of KFS makes a posterior occipitocervical fixation strategy challenging. For these patients, the transoral atlantoaxial reduction plate (TARP) operation is an optimal option to perform a direct anterior fixation to achieve stabilization.

OBJECTIVE: To evaluate the effectiveness of TARP internal fixation for the treatment of BI with KFS. METHODS: Ten consecutive patients with BI and KFS who underwent TARP reduction and fixation from 2010 to 2012 were reviewed. Clinical assessment and image measurements were performed preoperatively and at the most recent follow-up. Nine patients (9/10) were followed for an average of 31.44 months.

RESULTS: Symptoms were alleviated in 9 of 9 patients (100.00%). The odontoid process was ideally corrected with the TARP system. The mean clivus canal angle improved from 124 preoperatively to 152 postoperatively. The average preoperative and postoperative Japanese Orthopedic Association scores were 10.56 (n = 9) and 14.67 (n = 9), respectively, indicating 63.82% improvement. There was bony bridge catenation on the computed tomography scans and no evidence of hardware failure at 6 months.

CONCLUSION: The TARP operation is effective and safe for treating patients with BI with KFS. The midterm clinical results were satisfactory.

RESULTS: There was 1 death in the series, and 3 patients were lost to follow-up. The follow-up period ranged from 12 to 52 months (mean: 35.2 months) for the remaining 170 patients. Neurological improvement was observed in 168 of 170 patients (98.8%), and was stable in 1 (0.06%) and exacerbated in 1 (0.06%), with the Japanese Orthopedic Association scores increasing from 11.4 preoperatively to 15.8 postoperatively (P , .01). Radiologically, complete or .90% reduction was attained in 107 patients (62.9%), 60% to 90% reduction was attained in 51 patients (30%), and ,50% reduction was attained in 12 patients (7.1%), who underwent additional transoral decompression. Complete decompression was demonstrated in all 170 patients. Solid bony fusion was demonstrated in 167 patients at follow-up (98.2%).

CONCLUSION: This series showed the safety and efficacy of the posterior C1-2 facet joint release and reduction technique for the treatment of AAD and BI. Most fixed AAD and BI cases are reducible via this method. In most cases, this method avoids transoral odontoidectomy and cervical traction. Compared with the occiput-C2 screw method, this short-segment C1-2 technique exerts less antireduction shearing force, guarantees longer bone purchase, and provides more immediate stabilization.

RESULTS: Fourteen SAC were diagnosed prenatally (39%). We observed 15 (43%) cases presenting hydrocephalus (SAC-1) removing Liliequist membrane downward. Lower forms (SAC-2) with free third ventricle were observed in 11 (31%) cases. Asymmetrical forms (SAC-3) with Sylvian or temporal extension were seen in the 9 (26%) remaining patients. Twenty-three (66%) patients were treated by ventriculocisternostomy, 3 (8.5%) by shunt surgery, and 3 (8.5%) by craniotomy. Six (17%) patients had no surgery, including 5 cases (14%) that had prenatal diagnosis. Outcomes were initially favorable in 26 cases (87%). Eight (22%) patients had endocrine abnormalities at the end of the follow-up, 3 (8.5%) had developmental delay, and 6 (17%) had minor neuropsychological disturbances.

CONCLUSION: SAC are heterogeneous entities. SAC-1 may come from an expansion of the diencephalic leaf of the Liliequist membrane. SAC-2 show a dilatation of the interpeduncular cistern and correspond to a defect of the mesencephalic leaf of the Liliequist membrane. SAC-3 correspond to the asymmetrical forms expanding to other subarachnoid spaces. Surgical treatment is not always necessary. The recognition of the different subtypes will allow choosing the best treatment option.

Patients with Chiari malformation type 1 (CMI) often present with elevated pulsatile and static intracranial pressure (ICP). The preferred treatment of CMI, foramen magnum decompression (FMD), is assumed to normalise ICP and craniospinal pressure dissociation. In order to further explore the mechanisms behind FMD, the present study investigated whether or not pulsatile and static ICP normalises immediately after FMD.

Method The study included CMI patients undergoing FMD with perioperative ICP monitoring as a part of clinical management. The pulsatile and static ICP scores were retrieved from the department’s ICP database, and the clinical and radiological data from the patient records.

Results Eleven patients were included in the study. During the first 3 days following FMD, mixed model analysis revealed no significant time-dependent differences of preoperatively elevated either pulsatile (mean wave amplitude,MWA; p=0.85) and/or static (mean ICP, p = 0.90) ICP. Percentage of mean ICP >15 mmHg increased during days 2 and 3 after FMD. Two patients from the present series had to receive ventriculoperitoneal shunt after FMD in the early postoperative period.

Conclusions The present observations suggest that anatomical restoration of cerebrospinal fluid pathways by FMD does not lead to immediate normalisation of preoperatively altered pulsatile and static ICP in patients withCMI. This finding may explain persistent symptoms during the early period after FMD.

Chiari malformation type I is defined as a descent of cerebellar tonsils below the level of the foramen magnum. The traditional treatment for symptomatic patients is foramen magnum decompression (FMD) surgery. Intraoperative neurophysiological monitoring (INM) is an established surgical adjunct, which is proposed to reduce the potential risk of various surgical procedures. Though INM has been suggested as being helpful in patient positioning and in determining the optimal surgical extent of FMD (i.e., duroplasty, laminectomy, tonsillectomy), its shortcomings include prolongation of anesthesia and surgery as well as monetary costs. Multimodality INM including transcranial-electric motor evoked potential (TcMEP) is not routinely employed in most practices. This study evaluates efficacy of multimodality INM during FMD.

Methods This work is a retrospective analysis of prospectively collected data. Twenty-two FMD surgeries in 21 pediatric patients (aged 1–18 years) were performed at our center utilizing multimodality INM. All patients presented Chiari malformation type I, 18 of which had presented with syringomyelia, underwent posterior fossa decompression (FMD+ C1 laminectomy), accompanied in some with additional cervical laminectomies, duroplasty, and partial tonsillectomies. TcMEP and somatosensory evoked potentials (SSEP) were monitored throughout the procedure including before and after positioning. INM alarms were correlated with perioperative and long-term patient outcomes.

Results INM data remained stable during 19 operations. Three cases displayed significant attenuation in the monitoring signals, all concomitant with patient positioning on the surgical table. One case showed attenuation in SSEP data only, which remained attenuated following repositioning. Another displayed altered TcMEP concomitant with positioning which partially stabilized following repositioning and resolved following bony decompression. The third case showed unilateral attenuation of both TcMEP and SSEP data, which did not rectify until closure. In each of these three cases, no new neurological deficits were observed post operatively.

Conclusions Multimodality INM can be useful in FMD surgery, particularly during patient positioning. TcMEP attenuations may occur independent of SSEPs. The clinical implications of these monitoring alerts have yet to be defined. There is a need to establish an optimal, cost-effective monitoring protocol for FMD.

Surgical indications for patients with pineal cysts are controversial. While the majority of patients harboring a pineal cyst require no treatment, surgery is a well-accepted option for a subset of those patients with secondary hydrocephalus or Parinaud’s syndrome. The majority of pineal cysts are identified incidentally during workup for other potential conditions, which may or may not be related to the presence of the cyst. In the absence of clear obstruction of CSF pathways, the treatment of presumed symptomatic pineal cysts is debatable. To clarify the role of surgery in these borderline cases, the authors reviewed their experience with resection of pineal cysts in the absence of ventriculomegaly or Parinaud’s syndrome.

Methods The authors retrospectively reviewed medical records and imaging of all patients surgically treated between 2001 and 2014 with a pineal cyst in the absence of ventriculomegaly and Parinaud’s syndrome. The presenting symptoms, preoperative cyst size, preoperative radiographic aqueductal compression, extent of resection, and radiographic and clinical follow-up were documented.

Conclusions: The authors’ results suggest that ventriculomegaly and Parinaud’s syndrome are not absolute requisites for a pineal cyst to be symptomatic. Analogous to colloid cysts of the third ventricle, intermittent occlusion of cerebrospinal fluid pathways may cause small pineal cysts to become intermittently symptomatic. A select cohort of patients with pineal cysts may benefit from surgery despite a lack of hydrocephalus or other obvious compressive pathology.

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Suboccipital cough-induced headaches are considered a hallmark symptom of Chiari malformation type I (CMI). However, non–Valsalva-related suboccipital headaches and headaches in other locations are also common in CMI. The diagnostic significance and the underlying factors associated with these different headaches types are not well understood.

OBJECTIVE: To compare cranial morphology and hydrodynamics in 3 types of headaches in CMI to better understand the pathophysiological basis for the different headache characteristics.

CONCLUSION: Valsalva-induced worsening of occipital headaches appears to be related to a small intracranial volume rather than the smaller posterior cranial fossa. This explains the reduced intracranial compliance and corresponding higher pressure measured in CMI patients with headaches affected by Valsalva maneuvers.

The authors completed a prospective, institutional review board–approved study using intraoperative MRI (iMRI) in patients undergoing posterior fossa decompression (PFD) for Chiari I malformation. The purpose of the study was to examine the utility of iMRI in determining when an adequate decompression had been performed.

Methods Patients with symptomatic Chiari I malformations with imaging findings of obstruction of the CSF space at the foramen magnum, with or without syringomyelia, were considered candidates for surgery. All patients underwent complete T1, T2, and cine MRI studies in the supine position preoperatively as a baseline. After the patient was placed prone with the neck flexed in position for surgery, iMRI was performed. The patient then underwent a bone decompression of the foramen magnum and arch of C-1, and the MRI was repeated. If obstruction was still present, then in a stepwise fashion the patient underwent dural splitting, duraplasty, and coagulation of the tonsils, with an iMRI study performed after each step guiding the decision to proceed further.

Results Eighteen patients underwent PFD for Chiari I malformations between November 2011 and February 2013; 15 prone preincision iMRIs were performed. Fourteen of these patients (93%) demonstrated significant improvement of CSF flow through the foramen magnum dorsal to the tonsils with positioning only. This improvement was so notable that changes in CSF flow as a result of the bone decompression were difficult to discern.

Conclusions The authors observed significant CSF flow changes when simply positioning the patient for surgery. These results put into question intraoperative flow assessments that suggest adequate decompression by PFD, whether by iMRI or intraoperative ultrasound. The use of intraoperative imaging during PFD for Chiari I malformation, whether by ultrasound or iMRI, is limited by CSF flow dynamics across the foramen magnum that change significantly when the patient is positioned for surgery.

Understanding that atlantoaxial instability is the cause of Chiari malformation (CM), the author treated 65 patients using atlantoaxial stabilization. The results are analyzed.

Methods Cases of CM treated using atlantoaxial fixation during the period from January 2010 to November 2013 were reviewed and analyzed. Surgery was aimed at segmental arthrodesis.

Results The author treated 65 patients with CM in the defined study period. Fifty-five patients had associated syringomyelia. Forty-six patients had associated basilar invagination. Thirty-seven patients had both basilar invagination and syringomyelia. Three patients had been treated earlier using foramen magnum decompression and duraplasty. According to the extent of their functional capabilities, patients were divided into 5 clinical grades. On the basis of the type of facetal alignment and atlantoaxial instability, the patients were divided into 3 groups. Type I dislocation (17 patients) was anterior atlantoaxial instability wherein the facet of the atlas was dislocated anterior to the facet of the axis. Type II dislocation (31 patients) was posterior atlantoaxial instability wherein the facet of the atlas was dislocated posterior to the facet of the axis. Type III dislocation (17 patients) was the absence of demonstrable facetal malalignment and was labeled as “central” atlantoaxial dislocation. In 18 patients, dynamic images showed vertical, mobile and at-least partially reducible atlantoaxial dislocation. All patients were treated with atlantoaxial plate and screw fixation using techniques described in 1994 and 2004. Foramen magnum decompression or syrinx manipulation was not performed in any patient. Occipital bone and subaxial spinal elements were not included in the fixation construct. One patient died, and death occurred in the immediate postoperative phase and was related to a vertebral artery injury incurred during the operation. One patient had persistent symptoms. In the rest of the patients there was gratifying clinical improvement. More remarkably, in 7 patients, the symptoms of lower cranial nerve paresis improved. No patient worsened in their neurological function after surgery. Reductions in the size of the syrinx and regression of the CM were observed in 6 of 11 cases in which postoperative MRI was possible. During the follow-up period, there was no delayed worsening of neurological function or symptoms in any patient. Sixty-three patients improved after surgery, and the improvement was sustained during the average follow-up period of 18 months.

Conclusions On the basis of outcomes in this study, it appears that the pathogenesis of CM with or without associated basilar invagination and/or syringomyelia is primarily related to atlantoaxial instability. The data suggest that the surgical treatment in these cases should be directed toward atlantoaxial stabilization and segmental arthrodesis. Except in cases in which there is assimilation of the atlas, inclusion of the occipital bone is neither indicated nor provides optimum stability. Foramen magnum decompression is not necessary and may be counter-effective in the long run.

Chiari malformation type I (CMI) is characterized by deformed hindbrain. This study aimed to quantitatively evaluate the alterations in position of hindbrain after Posterior fossa decompression (PFD), and to identify the factors associated with syrinx resolution in pediatric patients with CMI.

Methods Eighty-seven patients, aged from 5 to 18 years, who underwent PFD for CMI between September 2006 and September 2012 were retrospectively reviewed. On midsagittal MR images, the position of medulla oblongata and cerebellum was quantitatively evaluated preoperatively and at follow-up. The maximal syrinx/cord (S/C) ratio and syrinx length were also measured. Significant improvement of syrinx was defined as a more than 20 % decrease in maximal S/C ratio or length on follow-up MRI.

Results Neurological deficits were found in 51 of the 87 patients preoperatively and 37 (72.4 %) of them obtained improvement of their symptoms at the last visit. Overall, upward shifting of the tip of cerebellar tonsil was observed in 66 (75.9 %) patients at the last follow-up. Moreover, the mean longitudinal distance of the tip of cerebellar tonsil changed from 16.47 ± 5.00 to 13.89 ± 4.38 mm (P<0.001) at final follow-up. Significant syrinx resolution was noticed in 79 (90.8 %) cases. Pointed cerebellar tonsils were found in 85 (97.7 %) of our patients preoperatively and 78 (91.8 %) of them acquired round cerebellar tonsils after PFD. The improvement of maximal S/C ratio was significantly correlated with upward shifting of the tip of cerebellar tonsil (P = 0.023).

Conclusions Following PFD for CMI, position and morphology of the cerebellar tonsil could revert to normal in most of the pediatric patients, and the upward shifting of the tip of cerebellar tonsil is significantly correlated with syrinx improvement. From this study, PFD without shunting may be effective for syrinx secondary to CMI in pediatric population.